Water is precious, and it is a factor in every aspect of oil production in the Permian Basin. It is used to produce the hydrocarbons, and it is produced with them. In the often-arid region of the Permian, finding a balance between water production and use can be a challenge.
“Water demand is very high in the Permian because we’ve drilled a lot of wells and the water intensity per foot of lateral is high,” said Bridget Scanlon, senior research scientist at the Jackson School of Geosciences at The University of Texas at Austin. Adding to the problem, she said, is that the primary source of water is groundwater, “which may be locally scarce.”
Scanlon presented a talk online with SPE that revolved around her recently published paper “Will Water Issues Constrain Oil and Gas Production in the United States?”
“Basically,” she said, “we emphasized that, to partially mitigate water-sourcing issues and disposal issues in the Permian Basin and in other places, it’s best to use the produced water for hydraulic fracturing.”
Using the produced water for hydraulic fracturing, however, presents a set of challenges, although some hurdles have been cleared. “Industry has developed techniques so that it now can use clean brine for hydraulic fracturing,” Scanlon said, “which makes this much more favorable.”
Other challenges involve the handling and storage of the produced water before using it for fracturing. “If you want to link the produced water to the hydraulic-fracturing-water demand, you need to store that water and transport it with pipelines,” she said, “so there may be increased risk of contamination of storing and transporting produced water that would need to be considered.”
Compounding the challenges are variances in water production and use from location to location. For instance, looking at the ratio of produced water to water used for hydraulic fracturing in the Midland Basin, “the two are fairly closely matched,” Scanlon said, “however, I understand that we need to match those at a local scale in order to make this happen.” In the Delaware Basin, the produced water exceeded the water used for hydraulic fracturing almost by a factor of two in 2018. “So, even if we were able to use all the produced water, we would still have an excess of produced water to be managed,” she said.
Other options for the water have been considered, including irrigation, municipal use, and groundwater recharge, although Scanlon cautions that “produced water volumes would not substantially alleviate water-scarcity issues.”
To be beneficial for irrigation, the produced water would need to be close to the irrigation areas. “Areas of produced water and irrigation are not generally collocated,” Scanlon said. “In counties (in the Permian) with large irrigation … we found that the excess produced water would constitute less than 10% of the irrigation-water demand.”
Scanlon said that, between 2005 and 2015, approximately 40 billion bbl of water was produced from conventional reservoirs. Most of that produced water, 36.5 billion bbl of it, was put back into the pressure-depleted reservoirs through enhanced-oil-recovery injection wells, “so it’s not really available for other uses,” she said. “We produced 4 billion bbl from unconventional reservoirs, and that water went into saltwater disposal wells in different units. So, we generated much more produced water from conventional reservoirs than unconventional reservoirs. In recent years, produced water from unconventional reservoirs has been increasing, but it’s still less than that from conventional reservoirs.”
Reinjecting produced water is a common technique for handling it, but that comes with its own set of challenges, including contamination and earthquakes from induced seismicity. Scanlon said that, in the Delaware Basin, 80% of the reinjected produced water is placed in shallow reservoirs that are above the oil and gas reservoirs. “So, this should reduce the risk of induced seismicity by putting it in shallow units,” she said.
Although reinjecting produced water to shallow reservoirs can mitigate the risk of induced seismicity, it creates other challenges. “Focusing on the shallow units may result in impacting overlying aquifers because of overpressuring and other issues,” she said. “And, also, they have to drill through those units to get to the reservoirs. For example, in the Midland Basin, they have to put extra casing strings sometimes … . So, there are trade-offs to going mostly shallow vs. deep.”
Reinjecting water into shallow reservoirs runs the risk of overpressuring those reservoirs, which could result in surface contamination. “This water will come up through salt … and could bring up salt into the aquifers,” Scanlon said. She added that abandoned wells can provide a pathway for that salty water to contaminate surface water. Approximately 30% of the wells that have been drilled in the Delaware and Midland basins have been abandoned, she said. “These can provide pathways for overpressured fluids that could contaminate overlying aquifers.”
Surface spills also can cause contamination problems. Scanlon said that surface water spills in New Mexico related to conventional wells are greater than those related to unconventional wells. Between 2009 and 2018, 5,000 produced-water spills were recorded in New Mexico related to conventional activity, compared with 1,150 related to unconventional activity. The main sources were pipelines and tanks, and the main causes were equipment failure and corrosion. Texas, however, does not record water spills.
Taking all these challenges into account, Scanlon concluded that the best use for produced water is hydraulic fracturing, although greater infrastructure is needed to move and store the water. Putting the produced water to use in other ways, she said, needs much more research to address the risks.
“There is a lot of confusion about produced-water volumes and where the produced water is coming from,” she said. “Some people think that we’re producing so much water in the Permian Basin that we can use it to recharge the aquifers and make them great again. But we need to understand how much produced water is coming from which type of reservoir and what it’s being used for and how much might be available for beneficial use in other sectors.”
